The present invention is directed to an explosive powder charge operated setting tool with a piston guide for a piston which can be driven from a rear starting position into a front end position by propellant gases generated when an explosive powder charge is ignited. A carrier including a cartridge receptacle is located at a rear end of the piston guide and a housing part laterally encloses and is spaced radially outwardly from the piston guide. A channel is located between the piston guide and the housing part and discharges through an opening in the front end of the piston guide into a guide bore for the piston.
In explosive powder charge operated setting tools of the above type, a piston is driven by propellant gases from an ignited explosive powder charge and the piston is propelled from a rear starting position into a front end position. Prior to ignition, the explosive powder charge is fed into a cartridge receptacle. Before reaching the front end position, the piston impacts on a bolt, nail or similar fastening element, and drives the element into a hard receiving material, such as concrete, metal and the like.
To position the piston for another driving step after it has been driven forwardly and the driving step has terminated, it must be returned from its front end position into its rear starting position. Mechanical arrangements are known for effecting the return travel of the piston. Such mechanical arrangements include pushing the piston rearwardly by a separate tappet or ram or displacing the piston guide relative to the piston in the driving direction and subsequently returning the piston guide along with the piston to the starting position. In all of these procedures, the piston reaches the rear starting position, however, these various mechanical arrangements for returning the piston involve the disadvantage of a considerable handling effort. This handling results in a loss of time which is particularly disadvantageous in rapid series driving of the fastening elements. Further, mechanically operated return devices are relatively malfunction-prone, particularly as a result of fouling caused by the propellant gases.
In place of mechanically operated return procedures, a return of the piston by the use of propellant gases is known, for instance in U.S. Pat. No. 3,744,240. In such a procedure it is known to enclose the piston guide serving to guide the piston spaced radially inward in the housing part. A carrier with a cartridge receptacle is located at the rear end of the piston guide. A channel connected to the cartridge receptacle is located between the housing part and the piston guide and conducts propellant gases in the setting direction and then through the opening in the piston guide into the guide bore for the piston.
In this known tool, the propellant gases act only in directly, that is, via an insertion piece, on the piston after the explosive powder charge has been ignited. The insertion piece forms a closure for the channel during the ignition of the powder charge. After the channel has been opened by the insertion piece, the propellant gases flow into the guide bore in front of the piston, where they are compressed and subsequently, as they expand, drive the piston back into the rear starting position. In this arrangement, the insertion piece must also be driven back into its rear starting position, whereby the channel is being closed in preparation for the next driving step. In this procedure there is the problem that the spaces must be adequately vented to enable the piston and the insertion piece to return to their rear starting position. This is possible only by disposing venting openings where even if slight contamination or clogging occurs adequate venting is no longer ensured and the entire operation of the return procedure is questionable. Thus the tool is not only very expensive in construction, but it also malfunction-prone and requires considerable maintenance and cleaning operations.